This invention relates to a novel pin bar and pin mold assembly and associated deck plate assembly for manufacturing capsules. More specifically, this invention relates to a pin bar and pin mold assembly and deck plate assembly for manufacturing methylcellulose pharmaceutical capsules.
Manufacture of hard shell gelatin capsules is carried out by a capsule-making machine. Typical of such capsule-making machines are those disclosed in U.S. Pat. Nos. 338,754; 1,787,777; 2,299,039; 2,568,094; 2,936,493; 3,632,700; 3,794,453; and 4,705,658. Capsule-making machines are divided into several sections, each section performing a different manufacturing step. A pin bar carries pin molds upon which capsules are formed. FIG. 1 shows a conventional stainless steel pin mold 10 mounted to a segment of a pin bar 12. The pin mold 10 has an extension 14 at one end which is fixedly mounted to the pin bar segment 12. The extension 14 has an outwardly sloping portion 16 that is rivetted into place in the pin bar segment 12. The pin bar passes through each capsule-making machine section and, at the end of the manufacturing cycle, delivers finished capsules.
To better understand the advance of the present invention, a method of manufacturing gelatin capsules in a conventional capsule-making machine follows. First, pin molds carried on a pin bar are lubricated in a greasing section of the capsule-making machine. The pin bar then passes to a dipping section. In the dipping section, pin bars are collected in groups and oriented with the pin molds facing downward. The pin bars are then lowered so that the pin molds dip into a liquid aqueous solution of gelatin, maintained at the proper consistency and temperature. The temperature of the gelatin solution is somewhat higher than the pin molds' temperature. The pin molds remain in the solution until a certain amount of the gelatin solution collects on each pin mold in a thin film. The pin bars are then lifted from the solution and moved laterally into an elevating device. The elevating device lifts the pin bars to an upper level in the machine and simultaneously rotates them through the atmosphere to preliminarily cool and set the gelatin coating evenly. The pin bars are then moved through a kiln section across a series of deck plates, or, in more recent machine designs, rollers, toward the back of the machine. Where deck plates are used, the deck plates are typically relatively thin steel sheets of plain carbon steel. At the far end of the kiln section, the pin bars are lowered from the upper level of the kiln section to a lower level. The pin bars pass forward through the kilns to a table section where gelatin film drying is completed. In the table section, individual pin bars are turned on their sides with the pin molds pointing horizontally outward. The pin bars are then pushed into an automatic section where the dried capsule films are stripped from the pin molds, and knives trim excess gelatin from the open ends of the films. The capsule films are then mated together, or joined, and the complete capsules are dropped onto a conveyor which carries them to suitable receptacles. After the capsules have been stripped from the pin molds, the pin bars move out of the automatic section and into the greasing section where the manufacturing process starts anew.
Since the introduction of hydroxypropylmethylcellulose ethers, more commonly known under the trademark METHOCELS, attempts have been made to convert or modify conventional gelatin capsule-making machines to produce methylcellulose capsules. The need in the worldwide marketplace for non-gelatin, kosher pharmaceutical capsules has spawned these attempts.
Companies experimenting in this direction have enjoyed only limited success in forming methylcellulose capsules on conventional pin molds used to form gelatin capsules. Gelatin and methylcellulose require different manufacturing parameters because these materials gel at different temperatures. Gelatin solutions liquefy when hot and gel as they cool. Hence, gelatin capsules may be dip-formed on relatively cool pin molds. Methylcellulose solutions, however, liquefy when cool (around room temperature or 70 degrees Fahrenheit) and gel at about 150-180 degrees Fahrenheit, depending on the solution's chemical properties. Thus, the pin molds must be heated prior to dipping to form methylcellulose capsules. Moreover, after dipping, the pin molds must remain heated during the manufacture cycle, at times up to 175 degrees Fahrenheit, until sufficient moisture is eliminated from the methylcellulose capsule films on the pin molds.
Maintaining conventional pin molds at sufficiently high temperatures to form methylcellulose capsules has proven problematic. For example, conventional pin molds generally are composed of solid, food-grade, 304 and 316 stainless steels which are particularly resistant to absorption of heat as compared to other steels. An additional problem with stainless steel is that it absorbs heat non-uniformly and thus would result in unevenly formed methylcellulose capsule films.
In the past, companies attempting to modify gelatin capsule-making machines into ones capable of making methylcellulose capsules blow high heat at the pin molds in the machine's kiln sections. This heat theoretically dries, or cooks, the methylcellulose from the outside inward. Deck plates in the kilns which carry the pin bars may be heated to raise the temperature of the pin bars prior to dipping. These deck plates are heated to a uniform temperature and apply that heat to the base and exterior of the pin mold.
A significant problem with prior kiln sections and deck plates, and the outside-to-inside manner of heating the stainless steel pin molds to make methylcellulose capsules, is that externally induced heat dissipates quickly from the surface of the pin molds and pin bars and thus is inefficient and costly. Moreover, the pin molds are often heated unevenly, resulting in thinning or deformation of the methylcellulose capsules. Irregularly shaped capsules jam automatic capsule filling machines.
Another source of inefficiency of external heat transfer to the pin molds via primarily heated, or superheated, air is that heat loss occurs rapidly as a result of the high polish of the pin molds. In addition, methylcellulose deposited onto the pin during dipping acts as a kind of thermal barrier, or insulator, further reducing efficiency when hot air is applied directly to the outside surface of the pin mold. And, because the kiln section is convection heated to temperatures above 150 degrees Fahrenheit, workers manning the machine feel extreme discomfort from the heat. Some of the heat generated in the kiln section vents outside of the kiln, making for poor work conditions.
Finally, externally induced heat tends to heat only the outside surface of conventional pin molds because of the relative heat conduction inefficiency of stainless steel relative to other materials, such as aluminum, copper, silver, and gold. Therefore, the pin mold becomes only superficially heated, or only heated on its surface. Meanwhile, the relatively "cool" core of the stainless steel pin mold quickly and continuously absorbs the heat induced onto the pin mold's surface, thus cooling the surface below the optimum thermal gelation temperatures for methylcellulose.
Additional patents known to applicant but believed to be peripheral in relevance to the present invention are the following: U.S. Pat. Nos. 1,527,659 and 4,247,006.
The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which may reduce the capability of prior pin molds, pin bars, deck plates, and the current modifications associated with capsule-making machines to manufacture methylcellulose capsules. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such methods and apparatuses appearing in the past will admit to worthwhile improvement.